Recent air pollution peaks, occurring in various parts of the world, have frequently been highlighted in the news. According to the World Health Organization (WHO), air pollution involves the contamination of indoor or outdoor environments by any chemical, physical, or biological agent that alters the atmosphere’s natural features. It is widely acknowledged that air pollution affects the overall population’s health, but what about athletes? Are there specific risks tied to their activities? In preparation for the Paris Olympics, it’s essential to grasp the basics to better understand this vast subject: what are the most hazardous particles, and where does pollution primarily stem from? The WHO has categorized various pollutants and closely examined their physiological impacts.
Key pollutants include elements like suspended particulate matter (SPM) of varying sizes and chemical makeups. Particles measuring 20 μm in diameter (PM20) quickly settle, leaving few airborne except in emission areas. Common atmospheric suspended particles include PM10 (with diameters up to 10 µm), PM2.5, and ultrafine particles (PM<0.1 µm). The smaller the particles, the more significant the impact on our organs and the higher the likelihood of causing or worsening respiratory, cardiovascular, or other health issues. Being exposed to PM2.5, even at levels below current standards, can heighten risks of stroke, cognitive decline, dementia, Alzheimer’s, and Parkinson’s disease. Carbon monoxide (CO), a gas produced during the incomplete combustion of carbon-containing substances, is a common byproduct from motor vehicles, heating systems, incinerators, refineries, and various industries. As our red blood cells have a stronger affinity for carbon monoxide than oxygen (O2), it leads to a rapid decrease in blood oxygen levels, potentially resulting in fatality. Sulfur dioxide (SO2) originates from volcanic and industrial activities. Although emissions have significantly dropped in developed nations recently, this is not the case worldwide, particularly in places still heavily relying on fuel oil and high-sulfur diesel.
Sulfur dioxide exposure correlates with increased cardiovascular and respiratory hospital admissions and fatalities. Nitrogen oxides (NOx) stem from nitrogen-rich fuels, primarily due to road traffic and electric generators. Nitrogen dioxide (NO2) is a major contributor to secondary photochemical pollutants like ozone and PM10 or PM2.5 organic nitrate and sulfate particles. Volatile organic compounds (VOCs) can emerge from leaks in pressurized systems (natural gas, methane, etc.), exhaust systems, fuel evaporation (benzene, etc.), cigarette smoke, or household products. These can range from merely unpleasant odors to carcinogenic potential. More concerning is their breakdown in the atmosphere, influenced by sunlight and heat, leading to the formation of other harmful compounds like ozone. Ozone (O3) stands as one of the most prevalent atmospheric pollutants, created through chemical reactions between nitrogen oxides, carbon monoxide, sunlight, and hydrocarbons. Wind spreads ozone over large cities and nearby hills, particularly on sunny days. It irritates airways aggressively, leading to more hospital visits and deaths, especially among those with respiratory conditions. It also contributes to cognitive decline, dementia, and Alzheimer’s.
As research links pollution with health issues, WHO has established pollutant thresholds that shouldn’t be exceeded, forming the basis for an air quality index and useful guidelines applicable to physical activities. Air quality levels are color-coded from green (good) to dark purple (poor quality), with explanations available on official national or regional agencies’ websites. Different international organizations provide country-specific overviews. Athletes should exercise caution under certain conditions, indoors or outdoors. Gasoline or diesel combustion produces exhaust gases containing potentially harmful pollutants like carbon monoxide, nitrogen oxides, VOCs, and particulate matter. High temperatures can generate substantial ozone. Consideration should be given to brake and tire wear and friction with road surfaces. Forces or turbulence between tires and the ground release road surface particles into the air. Often positioned near main roads for accessibility and parking lots, stadiums can be polluted during events. The New Delhi marathon frequently runs under health-threatening conditions. Pesticide exposure risks are challenging to assess, as few studies have investigated this concerning sports activities.
However, a systematic review identified a rising cancer and Parkinson’s disease frequency among outdoor workers exposed to pesticides. A study on 682 US golf course managers also indicated an elevated cancer mortality rate, specifically prostate, large intestine cancer, non-Hodgkin’s lymphoma, and brain or nervous system tumors. The Intergovernmental Panel on Climate Change (IPCC), in its sixth report, predicts a roughly 30% increase in wildfires due to climate change, contributing to various health issues. Wildfires and megafires release significant carbon dioxide and other pollutants, with smoke traveling thousands of kilometers, spreading pollution. During the 2017 wildfires in Portugal and Spain, pollutants reached maximum measurement instrument limits, with Portugal’s daily PM concentrations exceeding European and national limits for 7-14 days. Australia’s “black summer” (2019-2020) wildfires lasted five months in the country’s east and south, affecting Melbourne Tennis Open players’ respiratory health. Canada’s megafires and the striking orange New York skyline in early June illustrate current “unbreathable” air scenarios restricting outdoor sports. 2020’s Australian Open faced similar smoke disruptions. In Europe, outdoor exercise exposure to particulate matter (including pollen in the spring) arises in temperate climates (autumn-winter-spring) and to ozone during warmer seasons (spring-summer).
Global warming increases allergenic pollen spread. Concerns arose over recreational fields and artificial lawns made from recycled tires containing polycyclic aromatic hydrocarbons, vulcanizers, plasticizers, antioxidants, and heavy metals. Inhalation, ingestion, and contact with these harmful residues present risks. These particles primarily risk inducing genetic mutations rather than immediate respiratory health problems. The quantities found on sports fields exceed legal or recommended safety thresholds, including some carcinogens. Furthermore, there are no guidelines to shield individuals from potentially harmful effects of numerous chemical substances in tire rubber. Indoor sports pose unique risks. Both indoor and incoming outdoor air contain small particles and ozone. Outside air often interacts with indoor surfaces. Recent but limited studies measured PM, VOC, and CO2 pollution in gyms, fitness centers, and indoor sports facilities. Their concentration largely depends on participant numbers, activity type, and ventilation. Activities like yoga, which tend not to resuspend particles, have less impact than others. High VOC concentrations might come from alcohol-based hand sanitizers, cleaning products, air fresheners, diffusers, or new equipment (mats, fitness gear, etc.) used in fitness centers. Certain athletes exhibit increased sensitivity compared to others. Studies on air pollutants’ effects on performance include examining athlete times over different seasons for specific races and tracking the best international marathon times. These findings are compared to local environmental and climate data. Particles like PM2.5 and PM10 appear to increase marathon and 5km run times (notably for women).
Two possible reasons include reduced VO2 max (the maximal oxygen consumption during exercise) and heightened effort perception. This correlation was identified even below WHO thresholds, but not always noticeable individually or in short-term studies. Each 10 µg/m3 PM10 increase prolonged female marathoners’ times by 1.4%, with effects more pronounced under higher pollution. For instance, during the 2014 Beijing Marathon, heavy pollution likely delayed an average marathoner by around 12 minutes compared to moderate pollution conditions. Ozone impacts performance notably, reducing achievements while increasing dropouts, sometimes by up to 50% during high concentrations. Although minor at low levels, one study estimated a 0.39% performance decrease with each approximately 20 µg/m³ ozone increase. Ozone and particles often combine their effects. A United States seven-year Ironman event analysis showed ozone affected swimming performance, while PM2.5 greatly impacted cycling and running. Every 20 µg/m³ ozone increase led to a 1% final average time rise, with each 1 mg/m³ PM2.5 rise adding 0.12%. Highly trained marathoners, finishing quicker, are less affected by pollutants. Similar findings apply to team sports. Poor air quality linked to distance covered, high-intensity efforts, and pass numbers decrease among Bundesliga and teenage footballers. Within the US National Football League, defense performance drops coincided with high PM2.5 levels. Professional referees aren’t immune; reported arbitration errors rise 11% per 1ppm carbon dioxide increase (three-hour average) and by 2.6% with PM2.5 (12-hour average). Despite overshadowing pollution effects, heat presents significant performance challenges.
However, pollution’s impact, while sometimes minor, can still influence podium placements or scores by mere seconds. In an increasingly hot, polluted environment, could future athlete selection favor those less pollutant-sensitive to enhance team performance? More importantly, will this research sway public health policy? This article explores these questions.